Improving the outlook for human cancer can only come from a better understanding of the molecular mechanisms that cause human cancer. An important connection can be made between TGF_ signaling and cancer. The long-term objective of this application is to elucidate the molecular mechanisms underlying TGF_ regulation and functions, and understand the molecular basis of how alterations in TGF_ responses lead to deregulation of growth control in human cancer. TGF_ can act as both a tumor suppressor and as a significant promoter of tumor progression, invasion and metastasis. At early stages of tumorigenesis, loss of TGF_ growth inhibitory responses is frequent in cancers. However, carcinomas often secrete excess TGF_ and respond to it by enhanced invasion and metastasis. The short-term strategy of our research is to focus on the molecular mechanisms underlying the regulation of TGF_ signaling by heat shock protein 90 (HSP90) in normal epithelial and tumor cells. Our preliminary studies have demonstrated, for the first time, HSP90 inhibitors (e.g. the polyketide geldanamycin and derivatives), potently block TGF_ responses. The unifying hypothesis of this proposal is that HSP90 is an essential molecular chaperone in maintaining active TGF_ signaling. To test this hypothesis, we will undertake biochemical and cell biological studies to determine how HSP90 regulates TGF_-mediated activation of downstream signaling pathways and physiological responses in normal and tumor cells. Considering the partial completion of the originally proposed studies and the two-year allotted time frame, two important specific aims are proposed to accommodate the scope reduction yet without sacrificing scientific significance: 1. To fully characterize the molecular interplay between HSP90 and TGF_ receptors;2. To investigate the effects of HSP90 inhibitors in blocking TGF_-induced EMT, invasiveness and tumor metastasis. The proposed studies should not only gain insights into the effects of HSP90 inhibitors on TGF_ growth-regulatory responses, but also provide invaluable information on the use of HSP90 inhibitors to treat human cancers.